Use a naming convention if it exists in your programming language / organization.

IMHO, it's very important to easily distinguish in code between:

1. Local variables (including arguments to functions) and instance variables. You are lucky if your IDE automatically displays variables of different scope using different colors /bold/italic (as my favorite Eclipse does), but if it doesn't - you can use, for example, the following practice:localVariable_privateInstanceVariable__privateStaticVariablePublicProperty